A handout photo provided by Samaritan's Purse shows Dr. Kent Brantly working at an Ebola treatment clinic in Foya, Liberia, June 23. Brantly and Nancy Writebol, who are now suffering from Ebola in Liberia, are being evacuated to the United States for treatment.

Dr. Kent Brantly, one of the two Americans who contracted Ebola in Liberia, received a dose of an experimental serum before he was flown to the United States for treatment, an aid organization that he works with said Sunday.

The aid organization, a Christian group called Samaritan’s Purse, said it was grateful for news that Brantly’s condition is improving. Earlier, the group had said there was only enough serum for one dose and that it went to Nancy Writebol, the other American infected. Writebol is to be flown to Atlanta this week and treated at Emory University Hospital, where Brantly is also being treated. There is no known cure for Ebola. Dr. Thomas Frieden, director of the Centers for Disease Control and Prevention, has said he does not know what treatment the group may be using. There are several in development.

Brantly’s wife, Amber, said Sunday that Brantly is in good spirits. She said in a statement that the family was “rejoicing over Kent’s safe arrival” and confident that he is getting the best possible care.